It is known that isomaltulose (palatinose, 6-O-α-D-glucopyranosyl-D-fructose) can be produced by means of a biotechnological process through enzymatic isomerization from sucrose. Isomaltulose is a physiologically valuable sugar, with increasing significance as a sucrose substitute in foodstuffs and related products. Isomaltulose is acariogenic and has a low glycemic index while having essentially the same energy content as sucrose. Isomaltulose has been approved for use in foodstuffs since 2005. Isomaltulose serves also as raw material for the production of the sugar alcohol isomalt, a racemic mixture of 1,6-GPS (6-O-α-D-glucopyranosyl-D-sorbitol) and 1,1-GPM (1-O-α-D-glucopyranosyl-D-mannitol) as well as modifications thereof, in particular 1,6-GPS- or 1,1-GPM-enriched mixtures.
In the known biotechnological systems, sucrose is not completely isomerized enzymatically to isomaltulose. Rather, further isomerization products and byproducts are generated. Trehalulose is an important further isomerization product.
Trehalulose (1-O-α-D-glucopyranosyl-D-fructose) as a further important isomer of sucrose can be found in nature, for example in honey and, like isomaltulose, is not cariogenic.
Both isomers, isomaltulose and trehalulose, are known for example from EP 1 424 074 A1 as hetero-disaccharides which, compared to sucrose in the small intestine of human and animal consumers, have a reduced hydrolysis rate and present themselves as advantageous food components, in particular such that can keep blood sugar levels under better control.
Isomaltulose and trehalulose are produced on a large scale by using enzymatic rearrangement of immobilized bacterial cells or fragments thereof. In this respect, the α1-α2-glycosidic bond existing between the monosaccharide units of the sucrose disaccharide is isomerized into an α1-α6-bond with isomaltulose or an α1-α1-bond with trehalulose, respectively. This rearrangement of sucrose into the two acariogenic disaccharides takes place by catalysis of the bacterial enzyme sucrose isomerase (E.C. 5.4.99.11, synonym: sucrose mutase, saccharose mutase, sucrose isomerase, isomaltulose synthase). Microorganisms that have sucrose isomerase activity and which can be used in biotechnological processes, are in particular Protaminobacter rubrum, Erwinia rhapontici, Pseudomonas mesoacidophila, Pantoea dispersa and Serratia plymuthica. Depending on the organism used and the reaction conditions, the result of this reaction is a product mix, which can contain not only the desired acariogenic disaccharides isomaltulose and trehalulose in different proportions but also possibly unwanted monosaccharides, for example glucose and/or fructose, as well as oligomers.
EP 0 483 755 B1 discloses methods for the production of compositions containing trehalulose and isomaltulose, for which purpose Pseudomonas mesoacidophila MX-45 (FERM-BP 3619) or Agrobacterium radiobacter MX-232 (FERM-BP 3620) is used to obtain a product containing predominantly trehalulose.
The use of enzymatic activities from Pseudomonas putida, Thermus ruber, Thermus aquatica or Pimelobacter for producing compositions containing predominantly trehalulose from solutions containing sucrose is known from EP 0 794 259 B1.
EP 0 091 063 A2 and EP 0 625 578 A1 disclose methods for the production of isomaltulose using immobilized bacterial cells, in particular Protaminobacter rubrum (CBS 574.77). The disclosed methods are based on a solution containing sucrose, which is transformed into a product containing predominantly isomaltulose but also trehalulose, using immobilized cells.
The disclosed methods are all characterized by a limited activity of sucrose isomerase, and where in particular for large-scale production of isomaltulose, trehalulose or both, an improved process efficiency is desirable, in particular a faster turnover rate and/or increased conversion rate and/or yield.
Therefore, the present invention aims to solve the technical problem to overcome the aforementioned disadvantages and in particular to provide a method, in the frame of which a conversion of sucrose to a product containing isomaltulose and/or trehalulose is achieved that is improved as compared to the prior art. In particular, it is an aim of the present invention to provide an increased turnover rate and/or an increased rate of conversion and/or yield.